Add to/from int serialization

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.36842% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 75.72%. Comparing base (706cebd) to head (9eac428).

Files	Patch %	Lines
hstrat/serialization/_col_from_int.py	92.85%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #138 +/- ## =========================================== - Coverage 97.71% 75.72% -22.00% =========================================== Files 627 630 +3 Lines 8621 8658 +37 =========================================== - Hits 8424 6556 -1868 - Misses 197 2102 +1905 ``` | [Flag](https://app.codecov.io/gh/mmore500/hstrat/pull/138/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthew+Andres+Moreno) | Coverage Δ | | |---|---|---| | [tests](https://app.codecov.io/gh/mmore500/hstrat/pull/138/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthew+Andres+Moreno) | `75.72% <97.36%> (-22.00%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthew+Andres+Moreno#carryforward-flags-in-the-pull-request-comment) to find out more.

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